Irene A. Garibotti

Spatiotemporal Pattern of Primary Succession in Relation to Meso-topographic Gradients on Recently Deglaciated Terrains in the Patagonian Andes

Abstract Vegetation in primary succession is influenced by multiple stochastic and environmental factors at different spatial and temporal scales. In this study we analyze the effect of meso-topographic heterogeneity on vegetation development following the retreat of Glaciar Seco in the southern Patagonian Andes. Composition and cover of algae, lichens, mosses, and vascular plants were recorded in 580 plots located in different topographic positions within a chronosequence of eight consecutive moraines. Sample plots were characterized by topographical and surface features. Spatiotemporal patterns in vegetation composition and their relationships to environmental factors were assessed by classification and ordination. We recognized eight communities that correspond to four major successional stages. The successional sequence is characterized by a physiognomic development from pioneer saxicolous lichens (first stage) to secondary colonizer lichens (second stage), followed by shrub colonization (third stage) and the development of Nothofagus spp. forests (fourth stage). Alternative successional trajectories on different topographic positions vary in the sequence of these four major successional stages, with the trajectories on the moraine ridge-top and base not going through some of the stages. A variance partition procedure shows that time since deglaciation and topographic position on the moraines account for comparable amounts of vegetation variance, emphasizing the importance of spatiotemporal analysis of vegetation development on heterogeneous landscapes. Broad trends in vegetation development follow environmental gradients. However, emergence and persistence of vegetation patterns can also be attributed to dynamic geomorphic processes such as moraine slope degradation affecting boulder distribution along the moraine foreslope. At the landscape scale, successional trajectories converge to a Nothofagus-dominated state, but significant variability remains in the understory due to the differential distribution of cryptogams along the moraine topographic gradient. Convergence is mostly related to the expansion of communities from more favorable sites towards the harsher moraine crest, but it is not a process of gradual deterministic changes along the different successional pathways.

Vegetation Development on Deglaciated Rock Outcrops from Glaciar Frías, Argentina

Abstract The retreat of glaciers during past decades has led to the emergence of large rock outcrops in many glaciated areas around the world. Primary succession of vegetation in glacier forelands has been described for many regions, but most studies have been conducted on glacial deposits, whereas deglaciated rock outcrops have received little attention. This study assesses the pattern of primary succession on a chronosequence of five rock outcrops exposed during the past 140 years by the retreat of Glaciar Frías in the Patagonian Andes, Argentina. Data on floristic composition and species cover for algae, lichens, ferns, bryophytes, and vascular plants were recorded on sampling plots. Ordination and classification analyses discriminate three major successional stages, each dominated by a different species assemblage, suggesting directional replacement of species in the succession. The pioneer stage is dominated by the crustose lichen Placopsis perrugosa, the mid-successional stage by a lichen-moss mat dominated by the moss Racomitrium lanuginosum, and the late-successional stage by a large diversity of vascular plants. The low density of Nothofagus dombeyi saplings in the late-successional site indicates that plant succession is still in progress 140 years after deglaciation. Progress in succession appears to be influenced by species life-cycle traits and facilitative interactions among species. The comparison of the successional processes between rock outcrops and unconsolidated glacial deposits suggests that the vegetation sequence is similar, but the rate of succession is slower on rock outcrops. The development of a ground lichen-moss cover, previous to the widespread colonization by vascular plants, accounts for the slower succession progress on rock outcrops. The establishment of Nothofagus stands takes at least 100 yrs longer on the rock outcrops than on glacial deposits. Under predicted climate warming, most Patagonian Andes glaciers will continue the retreat along steep bedrock slopes, where similar, long-term vegetation successional patterns to those observed on Glaciar Frías foreland will eventually occur.

Morphological study of the marine planktonic diatom Chaetoceros castracanei Karsten (Bacillariophyceae) from Antarctic waters, with a discussion on its possible taxonomic relationships

Abstract Phytoplankton samples were collected along the north coast of the Antarctic peninsula, the Weddell Sea and the Gerlache Strait, in different seasons in 1985, 1986, 1999, and 2000–2002. Chaetoceros castracanei Karsten, a fairly rare species was present in the samples; its morphology, taxonomy and distribution have not been recently investigated. This species occurred mainly from January to April, and was recorded with relatively high abundances in the Weddell Sea (up to 9.5=104 cells l-1). C. castracanei forms straight or slightly curved, short to long chains, with the terminal and intercalary setae pointing in the same direction. The apertures are very reduced, centrally constricted, and there are numerous chloroplasts in the cells including the setae. Electron microscopy studies showed that valves are randomly perforated by round poroids, costae on the valve are absent, and an excentric rimoportula is present in every valve of the chain; the setae are circular in cross section at the base, but become four-sided distally. Setae have perpendicular rows of elongate poroids, spines are arranged in spirals along the setae and the tips are very pointed. The intercalary setae are fused together in sibling valves. Chaetoceros impressus Jensen et Moestrup, recently described from Danish waters, appears to be conspecific with C. castracanei, and consequently we propose it as a synonym of the latter. The known distribution of Chaetoceros castracanei may be broadened to include Antarctic, subantarctic and Danish waters, and also possibly more temperate regions.

Concentraciomes de pilas de rocas en la cuenca superior del río Santa Cruz (Argentina)

Este trabajo presenta y caracteriza dos concentraciones de pilas de rocas identificadas en la margen sudoeste de la cuenca superior del rio Santa Cruz (Argentina), en la Estancia Bon Accord. La edad minima de estas estructuras es estimada a partir de analisis liquenometricos. Se recopila informacion sobre la existencia de este tipo de estructuras en la region patagonica. Por ultimo, se discuten algunas de las funciones hipoteticas de estas acumulaciones utilizando casos arqueologicos locales y de otras partes del mundo.

Seasonal diatom cycle in Anegada Bay, El Rincón estuarine system, Argentina

Seasonal variations in the composition and carbon biomass of diatoms and other phytoplankton groups were analyzed over two years, from December 1996 to January 1999, at a fixed station in Anegada Bay, within the El Rincón estuarine system (38–41°S). Phytoplankton communities characterizing the different seasons were identified by classification and detrended correspondence analyses. Diatom communities were highly speciose, with 117 species recorded during the two-year study. Three diatom species are new records for the Argentinean Sea (i.e., Minidiscus trioculatus (F.J.R. Taylor) Hasle, M. decoratus Chrétiennot-Dinet & Quiroga and Thalassiosira tealata Takano). Phytoplankton taxonomic composition and carbon biomass showed a strong seasonality, with two carbon (C) biomass maxima occurring in summer and winter (maximum concentration: 193 μ g C L−1). Summer blooms were mainly dominated by tychoplanktonic diatom species (Paralia sulcata (Ehrenberg) Cleve, Rhaphoneis amphiceros (Ehrenberg) Ehrenberg and Delphineis surirella (Ehrenberg) Andrews), probably resuspended from the sediments, and by the pelagic diatom T. hendeyi Hasle & Fryxell. The winter phytoplankton community was characterized by a high number of diatom species and a high carbon biomass of diatom resting spores. The occurrence of the winter bloom seems to be closely associated with the inoculation of the water column by diatom resting spores. Maximum diatom carbon biomass corresponded to periods of increased freshwater inflow, whereas seasonal variations in diatom taxonomic composition may be explained by the life-cycle strategies of the species. The taxonomic composition and temporal succession of phytoplankton communities in Anegada Bay are comparable with previous studies in Blanca Bay, suggesting relatively uniform phytoplankton seasonality over shoals in the El Rincón estuarine system.

Linking biological soil crust attributes to the multifunctionality of vegetated patches and interspaces in a semiarid shrubland

Fil: Garibotti, Irene Adriana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Nuevos Datos de Referencia para la Tasa de Crecimiento de Rhizocarpon Subg. Rhizocarpon en Patagonia

This paper presents the results from lichen size survey of genus Rhizocarpon subgenus Rhizocarpon performed on surfaces exposed during last century in arid Patagonian environments (Santa Cruz, Argentina). We surveyed the cemetery of Puerto Deseado City and rock surfaces exposed by the retreat of Tunel Glacier in Los Glaciares National Park, providing eight new reference sites to estimate the growth rate of these lichens. Growth rate estimations for subgenus Rhizocarpon are between 0,125 to 0,061 mm per year. These values agree with previous estimations for other portions of Patagonian steppe and exhibit significant difference with available estimations for wetter regions in the Patagonian Andes.